1. Field
The invention relates to a semiconductor light emitting element, and a method of manufacturing the semiconductor light emitting element.
2. Description of the Related Art
As one of methods for mounting a semiconductor light emitting element on a mounting substrate, a flip-chip mounting method has been known. The semiconductor light emitting element used for flip-chip mounting has an n-type semiconductor layer and a p-type semiconductor layer formed on a substrate such as sapphire. The semiconductor light emitting element further has an n-side electrode and a p-side electrode which are connected to the n-type semiconductor layer and the p-type semiconductor layer, respectively and are formed on the same plane side of the substrate. After setting the p-type semiconductor layer and the n-type semiconductor layer to face downward, the semiconductor light emitting element is mounted such that the p-side electrode and the n-type electrode are opposed to wiring electrodes on a mounting substrate.
At this time, a light extraction surface of the semiconductor light emitting element is provided on a substrate side which is an opposite side to a surface where the semiconductor layers are laminated. Therefore, a reflection member for reflecting light to the substrate side is provided on a semiconductor layer side.
For example, Patent Literatures, Japanese Patent Publication No. 2007-80924 A, Japanese Patent Publication No. 2006-245231 A or Japanese Patent Publication No. 2012-238823 A disclose semiconductor light emitting elements which are mounted by flip-chip mounting. The semiconductor light emitting element has a sapphire substrate on which the n-type semiconductor layer and the p-type semiconductor layer are laminated in that order. A metal reflection film is formed on an approximately entire upper surface of the p-type semiconductor layer. The metal reflection film is made of an Ag or an Ag alloy and has good reflectivity to, especially, visible light. Also, each semiconductor light emitting element disclosed in these Patent Literatures has a metal film which covers the metal reflection film to prevent Ag migration contained in the metal reflection film, and further has a p-side pad electrode on the metal film.
Further, each semiconductor light emitting element including the metal film disclosed in Japanese Patent Publication No. 2006-245231 A and Japanese Patent Publication No. 2012-238823 A is covered with an insulation film made of an oxide or a nitride except connection portions of pad electrodes with an outside.
The insulation film made of the oxide or the like and the metal film cannot necessarily have a good adhesion property. Problems such that the insulation film is peeled from the metal film and a gap is formed at the connection portions may occur. If the insulation film is peeled from the metal film or the gap is formed, the metal film deteriorates under moisture, oxygen and the like in an open air. Consequently, if a prevention function to Ag migration of the metal film lowers, Ag migrates and a function as the semiconductor light emitting element is damaged.
Further, the metal film which prevents the migration is formed in consideration of a barrier property to Ag and an adhesion property with the reflection film. For example, each semiconductor light emitting element disclosed in Japanese Patent Publication No. 2006-245231 A and Japanese Patent Publication No. 2012-238823 A has a bottom layer made of Ni, Pt, Ti in the metal film for preventing migration abutting on the reflection film. However, since reflectance to, especially, the visible light of these metals is relatively low, light cannot be reflected sufficiently on a surface where the metal film abuts on the semiconductor layer at an outer edge of the reflection film, and light extraction efficiency suffers due to the low reflectance.